Nutrition is considered a cornerstone of day-to-day treatment of childhood diabetes mellitus (DM). However, little is known regarding the role of nutritional factors in the natural history of diagnosed Type 1 (T1) DM in youth, including progression of [unreadable]-cell decline and the emergence of cardiovascular disease (CVD) risk factors. The proposed work is an ancillary study to the CDC/DDT and NIH/NIDDK funded SEARCH for Diabetes in Youth project, which is an ongoing multi-center, observational study of DM diagnosed in youth age 0-19 years. Using both cross-sectional and longitudinal designs, the overall goal of the SEARCH Nutrition Ancillary Study (SNAS) is to examine associations of nutritional factors with 1) the progression of insulin secretion defects, and 2) the presence of CVD risk factors in youth with Type 1 DM. Consistent with the objective of PAR-07-024, SNAS is a natural extension of the stated aims of SEARCH Phase 2, which focuses on the evolution of DM type-related characteristics including insulin secretion defects, and the evolution of risk factors for long term complications of DM. From SEARCH data, dietary intake in adolescents with DM falls far short of nutrition recommendations. Moreover, the prevalence of CVD risk factors is elevated among youth with Type 1 DM, compared to youth without DM. To rigorously examine nutritional factors as determinants of metabolic status of youth with Type 1 DM, we propose to 1) obtain new data on history of infant feeding practices by questionnaire, and 2) obtain new laboratory test results on selected nutrient biomarkers (plasma tocopherols, vitamin D, magnesium, and fatty acids) using stored samples from SEARCH participants, and 3) conduct a Diet Assessment Sub-study to advance our capacity to appropriately construct statistical models to address measurement error in dietary data. Specific Aim 1 is to evaluate nutritional factors as potential determinants of preserved beta call function in approximately 1140 youth with Type 1 DM confirmed by positive DM autoantibodies. Subjects for Specific Aim 1 will have had diabetes diagnosed in 2002 - 2005, with fasting C-peptide data available longitudinally from the ongoing SEARCH study. Additionally, a subset of these youth will have beta cell function measured longitudinally as mixed meal stimulated C-peptide. Specific Aim 2 is to evaluate nutritional factors in relation to CVD risk factors in approximately 2415 youth with Type 1 DM prevalent in 2001 or incident in 2002 - 2005, using both crosssectional and longitudinal analyses. Results will uniquely inform nutrition recommendations and future clinical trials of nutrition interventions for youth with DM. All SEARCH sites are included in this project. Our multidisciplinary team is led by Dr Elizabeth Mayer-Davis, a well-recognized expert in diet and diabetes who directed the original SEARCH diet assessment.